Ink jet printheads typically comprise a nozzle plate joined to a heater chip. During ink jet printhead manufacturing, it is known to inspect assembled printheads on a sampled basis to determine if the nozzle plates are being properly aligned relative to the heater chips. One known inspection technique involves viewing a circular fiducial provided on the heater chip through a circular inspection opening provided in the nozzle plate. If the nozzle plate covers a portion of the circular fiducial such that only a portion of the fiducial is visible through the opening, then an "out of alignment" condition exists. If the entire circular fiducial is visible through the inspection opening, then an "in alignment" condition exists.
Due to manufacturing tolerances, the size of the nozzle plate inspection opening will vary from a nominal size. It has been found that when alignment between the nozzle plate and the heater chip is adequate by a narrow margin, an improper "out of alignment" condition may be indicated if the inspection opening is less than the nominal size but greater than the lower limit dimension. Because of such errors, this inspection technique is not preferred.
It is desirable to obtain accurate assessments of alignment with respect to, for example, nozzle plates and heater chips in order to ensure good print quality in ink jet printers.